Composite molding process utilizing tackified fabric material

ABSTRACT

A quantity of fluid resin material is rendered into a flowable state without the use of solvents. The fabric then is beaded with at least one elongate bead of the flowable resin, wherein at least a portion of bead remains on the surface of the fabric to tackify the fabric and facilitate lay-up of the beaded fabric in the composite molding process. The fabric then is laid-up into a molding apparatus, wherein the bead adheres to surfaces in the molding apparatus and assists in positioning of the fabric therein. A further quantity of resin is disposed or injected under pressure into the molding apparatus and into contact with the fabric and contours of the mold. The resin then is cured to form the composite body.

BACKGROUND OF THE INVENTION

1. Field of the invention

The present invention relates generally to composite molding processesfor forming composite bodies that include a fabric. More specifically,the present invention relates to a process and product for improvingcomposite molding processes and the composite bodies resultingtherefrom.

2. Background Information

A number of composite molding processes for forming composite bodiesincluding a fabric are known. These processes, and the productsresulting from them, find utility in the aerospace industry and otherindustries where parts of complex shape having the combination of highstrength and low weight are advantageous.

One such composite molding process is resin transfer molding ("RTM"). InRTM precesses, a fabric material, such as fiberglass or woven carbonfibers, is placed on or laid-up in a die or mold tool having thecontours of the desired part therein. After the fabric is laid-up in themolding tool, the tool is placed in a molding press in which a resinmaterial is injected in a fluid state to impregnate and fill the fabricand cavities in the die or mold tool. After the resin is injected andcured, a composite body or part results that has excellent strength andgenerally low weight. RTM and similar composite molding processes alsoare very cost-effective.

If the die or molding tool possesses many contours, and particularlyupstanding walls, the lay-up of the fabric in the mold, prior to theresin injection step, is rendered difficult because the dry fabric doesnot adhere the contours of the die or mold tool, particularly toupstanding surfaces. If the fabric is not laid-up properly, theresulting composite body will not possess adequate strength due towrinkles or other imperfections in the laid-up fabric.

Prior-art solutions to this problem include tackifying, or renderingtacky, the fabric prior to the lay-up step of the composite moldingprocess. Generally, use of an adhesive in the tackifying process that ischemically different from the resin ultimately injected in the compositemolding process is unsatisfactory. This is because an adhesive havingchemical and other properties different from that of the injection resincan degrade the strength of the cured resin and the resulting compositebody.

As a general matter, most injection resins are too viscous in theiruncured state to be applied to a fabric to provide a satisfactorytackifying material. Therefore, prior-art tackifying processes haveemployed the injection resin, thinned with an organic solvent such asacetone, as the tackifying adhesive. The resin, thinned with the organicsolvent, is of a satisfactory consistency to provide tackification.However, as with adhesives chemically different from the injectionresin, the organic solvent present in the tackifying material degradesthe cured resin and the strength of the resulting composite body.

A prior-art alternative to the use of solvent with the injection resinas a tackifier is to provide the injection resin treated in such amanner that it is a fine powder. This powder can be applied to thefabric and serves as a tackifying adhesive. Once such product is andsold under the tradename AMD, sold by 3M Corporation of St. Paul, Minn.This product is a derivative of, and therefore chemically and otherwisecompatible with, the injection resin sold under the tradename PR500epoxy resin, also manufactured by 3M Corporation of St. Paul, Minn.However, because the AMD product is in a fine, powdered form, it becomesairborne easily, and could pose a respiratory health hazard. Currently,tackifying processes employing the AMD material are conducted in acontrolled environment with all operators wearing cumbersome respiratorequipment.

In addition to the inadequacy of prior-art tackifying materials, theprocesses employed in applying the tackifying material to the fabrichave been less than satisfactory. In prior-art processes, the tackifyingmaterial was applied by manual painting or spraying. These prior-artprocesses allow little or no control over the amount of tackifyingmaterial being applied to the fabric. Moreover, spraying the tackifyingmaterial causes it to become airborne, increasing the risk of arespiratory health hazard.

A need exists, therefore, for a process for tackifying fabric for use ina composite molding process that employs the unadulterated injectionresin as the tackifying material and that controls the amount oftackifying composition applied to the fabric. A need also exists for atackified fabric for use in composite molding processes.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide a compositemolding process for forming composite bodies including a fabric, whereinthe fabric is rendered tacky by application of the injection resin tothe fabric. It is a further object of the present invention to providean improved tackified fabric for use in a composite molding process.

These and other objects of the present invention are achieved byrendering a quantity of fluid resin material in a flowable state withoutthe use of solvents. The fabric then is beaded with at least oneelongate bead of the flowable resin, wherein at least a portion of beadremains on the surface of the fabric to tackify the fabric andfacilitate lay-up of the beaded fabric in the composite molding process.The fabric then is laid-up into a molding apparatus, wherein the beadadheres to surfaces in the molding apparatus and assists in positioningof the fabric therein. A further quantity of resin is disposed orinjected under pressure into the molding apparatus and into contact withthe fabric and contours of the mold. The resin then is cured to form thecomposite body.

According to a preferred embodiment of the present invention, thebeading step is accomplished by conveying the fabric past a beadingapparatus that includes a plurality of spaced-apart beading apertures,wherein the flowable resin is extruded onto and applied to the fabric ina plurality of spaced-apart, parallel beads.

According to a preferred embodiment of the present invention, the resinis a single-part epoxy manufactured by 3M corporation of St. Paul, Minn.and sold under the tradename PR500. The fabric may be fiberglass orcarbon fibers.

According to a preferred embodiment of the present invention, prior tothe laying step, a sheet of protective material is disposed over thebeaded surface of the fabric, thereby protecting the beads and providinga tackified material for subsequent use in a composite molding process.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a composite molding process ofthe type contemplated by the present invention.

FIG. 2 is a side elevation view of the apparatus employed in practicingthe process of the present invention.

FIG. 3 is a front elevation view, partially in section, of the apparatusof FIG. 2.

FIG. 4 depicts the tackified fabric resulting from the process accordingto the present invention.

FIG. 5 illustrates the fabric of FIG. 4 in another embodiment of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1, a composite molding process of the typecontemplated by the present invention is schematically illustrated. Themolding process illustrated is commonly known as resin transfer molding("RTM"), but the process and product according the present inventionhave utility in a number of composite molding processes that are similarin many respects to RTM. In the composite molding process illustrated, aquantity of reinforcing fabric 1, typically fiberglass or woven graphiteor carbon fibers is provided. The fabric is laid-up into a die or moldtool 3, which contains the contours and surfaces of the final, finishedpart or composite body resulting from the process. Often, fabric 1 islaid-up into mold tool 3 in plys of varying shape and dimension toachieve a composite part or structure having a particular shape orstrength characteristic. Once fabric i is laid-up in mold tool 3, themold tool 3 is placed in a low-pressure molding press 5. A resin then isinjected into mold tool 3 to impregnate fabric 1 and fill cavities inmold tool 3. The resin then is permitted to cure, and mold tool 3 isopened to reveal a finished composite body or part 7.

If mold tool 3 possesses complicated geometry and especially upstandingwalls, the step of laying-up fabric 1 in mold tool 3 can become quitedifficult. If fabric 1 is not tackified or rendered tacky, it is quitedifficult to obtain a wrinkle-free lay-up and to maintain fabric 1 inclose contact with upstanding or convoluted surfaces of mold tool 3.

FIGS. 2 and 3 are side and front elevation views, respectively, of theapparatus employed in the process according to the present invention. Inaccordance with the process of the present invention, fabric 1 isconveyed past a beading apparatus 9 wherein beads of resin 11 are formedand applied to a surface of fabric 1. The conveying apparatus include asupply roll of fabric 13 and a supply roll 5 of protective material 7,such as polyethylene film that is of the same width or wider than fabric. Protective material 17 is applied to the underside of fabric at pinchroller 9. Fabric 1 and protective material 17 then are conveyed pastbeading apparatus 9, which deposits or extrudes onto fabric 1 at leastone bead 11 of flowable resin material substantially identical to thatused subsequently in the composite molding process. Beaded fabric thenis rolled on take-up roll 21 and another sheet of protective material 23from another supply roll 25 is placed over the upper, beaded surface offabric 1. The beaded fabric resulting from the process then may bestored, in conditions suitable for the uncured resin forming beads 11,for future use in the composite molding process.

According to a preferred embodiment of the present invention, the resinof which beads 11 are formed is a single-part epoxy resin sold under thetradename PR500 and manufactured by 3M Corporation of St. Paul, Minn.PR500 is preferred in aerospace applications because it has good curedstrength and is easily handled in the molding process. PR500 is chosennot for its characteristics as a tackifier, but because it is thepreferred resin used in the injection step ("injection resin") of theRTM process contemplated by the present invention. Other resins may beappropriate in the injection step, and thus may be used in the beadingstep according to the present invention.

With reference to FIG. 3, the construction of beading apparatus 9 isdescribed in detail. Beading apparatus 9 comprises an insulated cabinetor housing 31. A plurality of infrared lamps 33 are provided on theinterior of housing 31. A control valve 35 is disposed within housing 31and is connected to a resin extrusion pump (not shown) of the typecommonly used to inject resin in a mold apparatus. A preferred resinextrusion pump is manufactured by Venus-Gusmer and sold under thetradename RAM. Valve 35 serves as a means to selectively commence orhalt operation of beading apparatus 9. A pair of 0.375 inch O.D. copperfeeder lines 37 extend from valve 35 into fluid communication with abeading tube 39.

Beading tube 39 is constructed of 0.250 inch O.D. copper tubing that isplugged at both ends. Beading tube 39 is approximately as long as thewidth of fabric 1, preferably 42 inches. A plurality of beadingapertures 0.031 inch in diameter are spaced apart at approximately 1.5inch intervals along the length of beading tube 39. Resin is extrudedthrough these apertures to form beads 11. Beads 11 exit cabinet 31through 0.750 inch diameter apertures that are lined with removablesleeves 41. Removable sleeves 41 are provided so that they may be easilyreplaced if occluded with resin material during operation.

Cabinet 31 is provided to enclose beading tube 39 and related equipmentto maintain them, and the resin flowing therethrough, at a temperatureat which the uncured resin is flowable. At room temperature (72° F.),the PR500 resin has a viscosity of approximately 100,000 centipoise,which is too viscous to permit beading according to the presentinvention. Infrared lamps 33 serve to maintain the temperature insidecabinet at approximately 200° F. Maintenance of the PR500 resin atapproximately 200° F. in the RTM pump (not shown) and within cabinet 31renders the PR500 resin into a flowable state in which it may beextruded to form beads 11 according to the present invention.

Most resins employed in composite molding processes, like PR500, are tooviscous at room temperature to permit beading with the resin. Dependingon the resin employed, temperatures differing from those set forth abovemay be appropriate to render the resin into a flowable state for beadingfabric according to the process of the present invention.

As is readily understood, the speed of conveyance of fabric 1 pastbeading apparatus 9, together with the dimension of apertures in beadingtube 39, will dictate the dimension of beads 11. Preferably, beads 11are approximately 0.040 to 0.050 inch in width and no less than about0.030 inch in width. These bead dimensions can be obtained employing theforegoing aperture dimensions and a fabric velocity of approximately 20feet per minute relative to beading apparatus 9.

FIG. 4 depicts beaded fabric 100 according to the present invention.Beaded fabric 100 include a plurality of generally parallel,spaced-apart, elongate beads 11 on the upper surface thereof. Beads 11are maintained on the surface of fabric 1 (rather than impregnating orbeing absorbed by fabric) to provide an adhesive or tackifying materialto facilitate lay-up of fabric in mold tools of complex shape (3 in FIG.1). Beads of resin 11 preferably are continuous and extend the length offabric 1, and are spaced apart approximately 1.5 inch.

FIG. 5 depicts beaded fabric 100 according to another embodiment of thepresent invention. Commonly assigned U.S. Pat. No. 5,324,563, disclosespultruded rods formed of resin and carbon fiber that have compressivestrength vastly improved over the prior art. Among other uses, such rodsare useful as reinforcement in composite bodies formed by compositemolding processes. Such rods typically are laid-up between plys offabric to form a "sandwich" construction.

It has been found that pultruded rods must be maintained slightlyspaced-apart during the lay-up step and in the resulting composite body.If the rods are not slightly spaced-apart, but are in contact, thefriction between the rods degrades their strength and that of thecomposite body.

Beaded fabric 100 provides an excellent aid for laying-up pultruded rods150. Simply by laying rods 150 on the beaded surface of fabric, whereinrods 150 intersect beads 11, temporarily secures rods 150 to beadedfabric 100. By gently pressing rods 150 into resin beads 11, resinextrudes between rods 150 and insures that rods 150 are spaced apartsufficiently to insure their proper function. Beaded fabric 100 and rods150 then may be laid-up conventionally and beads 11 serve to facilitatethe lay-up step.

The process and product according to the present invention possess anumber of advantages. Specifically, the present invention facilitatescomposite molding processes involving complex shapes and/orincorporating pultruded rods without degrading the resulting compositebody.

The invention has been described with reference to preferred embodimentsthereof. It is thus not limited, but susceptible to variation andmodification without departing from the scope of the invention.

I claim:
 1. A composite molding process for forming composite bodiesthat include a fabric, the process comprising:rendering a quantity ofresin into a flowable state without the use of solvents; beading asurface of the fabric with at least one elongate bead of the flowableresin, wherein at least a portion of the bead remains on the surface ofthe fabric to tackify the fabric and facilitate lay-up of the beadedfabric in the composite molding process; laying the beaded fabric into amolding apparatus, wherein the bead adheres to surfaces in the moldingapparatus and assists in positioning of the fabric therein; disposing afurther quantity of the resin under pressure into the molding apparatusand into contact with the fabric; and curing the resin to form thecomposite body.
 2. The process according to claim 1 wherein the beadingstep further comprises:conveying the fabric past an extrusion apparatusincluding a plurality of spaced-apart extrusion apertures, wherein theflowable resin is extruded onto and applied to the fabric in a pluralityof spaced-apart, parallel beads.
 3. The process according to claim 1wherein the resin is an epoxy.
 4. The process according to claim 1wherein the fabric is fiberglass.
 5. The process according to claim 1wherein the fabric is woven of carbon fibers.
 6. The process accordingto claim 1 wherein further comprising the step of:prior to the layingstep, laying at least one pultruded rod on the surface of the beadedfabric and in contact with the bead, the pultruded rod being generallyat an angle relative to the bead.
 7. The process according to claim 1wherein the resin is heated to the flowable state.
 8. The processaccording to claim 1 further comprising the step of covering the surfaceof the beaded fabric with a sheet of protective material.
 9. A compositemolding process for forming composite bodies including a fabricmaterial, the process comprising:heating a quantity of resin to aflowable state in an extruding apparatus including a plurality ofspaced-apart apertures; conveying the fabric past the apertures in theextruding apparatus; and extruding the flowable resin through theapertures in the extruding apparatus and onto a surface of the fabric toform a plurality of spaced-apart, generally parallel, elongate beads,wherein at least a portion of the beads remains on the surface of thefabric; laying the beaded fabric into a molding apparatus, wherein thebeads adhere to surfaces of the molding apparatus and assist inpositioning of the fabric therein; injecting a further quantity of theresin under pressure into the molding apparatus and into contact withthe fabric: and curing the resin to form the composite body.
 10. Theprocess according to claim 9 wherein the resin is an epoxy.
 11. Theprocess according to claim 9 wherein the fabric is fiberglass.
 12. Theprocess according to claim 9 wherein the fabric is woven of carbonfibers.
 13. The process according to claim 9 further comprising the stepof:prior to the laying step, laying at least one pultruded rod on thesurface of the beaded fabric and in contact with and intersecting thebeads,
 14. The process according to claim 9 further comprising the stepof covering the surface of the beaded fabric with a sheet of protectivematerial.
 15. A composite molding process for forming composite bodiesof a fabric material, the process comprising:rendering a quantity ofresin into a flowable state without solvents in an extruding apparatusincluding a plurality of spaced-apart apertures; conveying the fabricpast the apertures in the extruding apparatus; and extruding theflowable resin through the apertures in the extruding apparatus and ontoa surface of the fabric to form a plurality of spaced-apart, generallyparallel, elongate beads, wherein at least a portion of the beadsremains on the surface of the fabric; laying at least one pultruded rodon the surface of the beaded fabric and in contact with and intersectingat least one of the beads; laying the beaded fabric into a moldingapparatus, wherein the bead adhere to surfaces of the molding apparatusand assist in positioning of the fabric therein; injecting a furtherquantity of the resin under pressure into the molding apparatus andcuring the resin to form the composite body.
 16. The process accordingto claim 15 wherein the resin is an epoxy.
 17. The process according toclaim 15 wherein the fabric is fiberglass.
 18. The process according toclaim 15 wherein the fabric is formed of carbon fibers.
 19. The processaccording to claim 15 further comprising the step of covering thesurface of the beaded fabric with a sheet of protective material.